1. Field of the Invention
The invention relates generally to lamps, and more particularly to the field emission lamps.
2. Description of Related Art
Electrical lamps are virtual necessities in modem daily living, and conventional electrical lamps generally include incandescent lamps and fluorescent lamps. A typical incandescent lamp is simple to manufacture. However, most electric energy consumed by the incandescent lamp is converted into heat energy and cannot be used for luminescence. In other words, the incandescent lamp has a low electrical energy utilization ratio, and is uneconomical.
A conventional fluorescent lamp has a higher electric energy utilization ratio compared to the incandescent lamp. A typical conventional fluorescent lamp generally includes a transparent glass tube, white or colored fluorescent material coated on an inner surface of the transparent glass tube, and mercury vapor filled in the transparent glass tube. In use, electrons are accelerated by an electric field so that the accelerated electrons collide with the mercury vapor. This causes excitation of the mercury vapor and subsequent remission. The remission process causes radiation of ultraviolet rays. The ultraviolet rays irradiate the fluorescent material, whereby the ultraviolet rays are converted into visible light.
The mercury vapor is toxic to humans and is environmentally unsafe. Thus, fluorescent lamps not adopting mercury vapor have been sought. FIG. 4 represents a conventional fluorescent lamp not using mercury vapor, as disclosed in China Patent No. 02234995.2. The fluorescent lamp includes a glass tube 1, fluorescent material 3 formed on an inner surface of the glass tube 1, a conductive film 2 formed on an outer surface of the glass tube 1, a pair of outer electrodes 5 located at opposite ends of the glass tube 1, and inert gases such as xenon vapor 4 filled in the glass tube 1. In use, high frequency alternating voltage is applied to the outer electrodes 5, thereby causing electrons to be accelerated therefrom. The accelerated electrons then collide with the xenon vapor 4. This causes excitation of the xenon vapor 4 and subsequent remission. The remission process causes radiation of ultraviolet rays. The ultraviolet rays irradiate the fluorescent material 3, whereby the ultraviolet rays are converted into visible light.
The above-described fluorescent lamp adopts inert gases such as xenon vapor instead of mercury vapor, and is thus safe for humans and environmentally friendly. However, adopting inert gases increases the cost of the fluorescent lamp. Furthermore, the inert gases are apt to leak out, and this results in the fluorescent lamp becoming dim or even failing to luminesce at all. Moreover, the fluorescent lamp generally adopts a hot cathode, and therefore needs a high working voltage. As a result, the electric energy utilization ratio of the fluorescent lamp may still be considered to be unsatisfactory.
What is needed, therefore, is a fluorescent lamp having a high electrical energy utilization ratio, low energy consumption, and a low cost.